1. Field
The inventive concepts relate to a method of forming a semiconductor device and, more particularly, to methods of forming a pattern and devices formed by the same.
2. Description of Related Art
As semiconductor devices are being increasingly integrated, finer patterning processes are demanded. A width of a photoresist pattern realized by an exposure process is determined depending on the following Rayleigh's equation.
[Rayleigh's Equation]R=k1×λ/NA 
In Rayleigh's equation, “R” denotes a resolution, “k1” is a process constant, “λ” denotes a wavelength of a light source, and “NA (numerical aperture)” denotes an effective aperture of a lens. Thus, in order to lower the resolution R, the process constant k1 may be reduced, the wavelength λ of the light source may be reduced, and/or the effective aperture NA of the lens may be increased. Exposure processes using extreme ultraviolet (EUV) having a wavelength of 13.4 nm as a light source are demanded in order to lower the wavelength of the light source than a wavelength (248 nm) of currently used KrF or a wavelength (193 nm) of currently used ArF. However, exposure processes using the EUV need environments (e.g., a vacuum state and reflective photomasks, etc.) different from those of conventional exposure processes, and exposure apparatuses using the EUV as a light source are relatively expensive. Thus, it is relatively difficult to apply the exposure processes using the EUV to manufacturing processes of semiconductor devices.
As described above, there are limitations in reducing the wavelength of the light source. Research has been conducted for increasing the effective aperture NA of the lens in order to lower the resolution R. The effective aperture NA is proportional to n×sin θ where “n” denotes a refractive index of a medium between the lens and a photoresist. Thus, if the refractive index of the medium is high, the resolution may be lowered. An immersion lithography process using this principle has been proposed. The immersion lithography process uses a conventional light source and is performed in a medium having a greater refractive index than air in order to improve a resolution characteristic. For example, water having a refractive index of 1.44 greater than air having a refractive index of 1 is used as the medium.